1. Field of the Invention
The present invention relates to automatic storage and retrieval systems generally, and more particularly to computer controlled, high throughput, industrial storage and retrieval systems.
2. Description of the Prior Art
Most industrial operations require on-site storage and retrieval of items. In the field of manufacturing, for example, a stock of the components of a manufactured item must be maintained on the premises and made available to a production or assembly line. For peak efficiency, component flow to the assembly line should be uninterrupted and should be paced to allow the assembly line to produce at their maximum capacity without having to wait for parts. The parts storage area must be space efficient, to minimize real property, building and heating and air conditioning costs, while, at the same time, being maximally accessible. An inherent conflict exists between space efficiency and ease of access since the surface area of a particular storage configuration, through which access is provided to the items stored within the space, is inversely proportional to volumetric efficiency. In addition, there is a competition between personnel and functions within the manufacturing environment for access to the stored goods, but it is, however, also desirable to be isolated from the clutter and activity associated with storage and retrieval facilities and functions. The feasibility of a particular spatial configuration and location of a storage area further depends upon the means of storage, e.g., bins, shelves, hooks, drawers, etc., the means for placing an item in storage, e.g., by hand, with a crane, with a forklift, etc., the means for retrieving an item from storage and the nature of the item stored.
Numerous strategies have been employed over the years for providing suitable storage and retrieval systems. Many have utilized bays of storage shelves upon which goods are stored and retrieved by a person (stocker). Frequently, large shelving systems require ladders, gantries and catwalks to permit stockers to gain access to items stored at higher levels. If high item throughput is required, an increased number of stockers seeking access to the stored items and utilizing the same catwalks and access aisles must be employed. Machinery under stockers' control, such as forklifts, are frequently employed to assist stockers by providing them with increased lifting power. This machinery, however, also increases the stockers' profile in the access channels to the storage area and thus increases congestion, slows throughput, and creates a safety hazard. Dumbwaiters, elevators, conveyor belts and other item transport means save stockers' steps but limit throughput to the speed of the transport means, which is frequently shared by several stockers. The storage and retrieval of items by human stockers is a labor intensive task, is often dangerous and repetitive, and sometimes results in the breakage of items padding through the system.
Besides the physical arduousness associated with the transfer of items to and from storage, a prime consideration in the material handling field is the maintenance of inventory records. A count of items on hand must be kept to trigger reordering of items before they run out. Either a running tally must to be maintained, requiring the constant, contemporaneous recordal of storage and retrieval transactions in a common record, or an exhaustive periodic inventory, wherein all items are counted, must be conducted. Both methods require significant time and effort. A record of the location of stored items must also be kept, or the items must be stored in a predetermined order, to facilitate retrieval.
Recently, automated storage and retrieval systems have been devised for remedying the limitations of traditional storage and retrieval systems. One type employs independently moving tiers of shelves that move radially around an oval track enabling items, or spaces for items, to be brought into proximity to an on/off load point. This device allows access to a storage space or an item by moving it to the stocker for storage/retrieval (placing/picking) rather than the stocker going to the storage space or item. Frequently, a robotic stocker or item handler (inserter/extractor) is utilized for transferring items to and from the movable shelves (placing/picking) from and to the on/off load point, which can be any supporting surface--including another means of conveyance such as a conveyor belt. Modern automated material handling systems typically utilize a computer controller for controlling and coordinating each mechanism in the system. Optic, acoustic and tactile sensors are used to sense the position of items and material handling mechanisms and relay this data to the computer controller which may then direct the activity of system machinery based upon the sensory input. Optical sensors for reading bar codes affixed to items, as well as, key entry terminals, allow computer controlled automatic storage and retrieval systems to constantly maintain and update item location and inventory records as item transfers occur.
An automated material handling system designed by Stanley Vidmar, Automated Systems is representative of state of the art techniques pertinent to the present invention. This system, appearing in the January, 1988 edition of AUTOMATION, includes parallel banks of stationary wire-rack storage shelves having a single aisle therebetween. A computer controlled robotic item handler (inserter/extractor) travels on tracks down the aisle between the shelf banks for placing/picking items carried in standard tote boxes to/from the wire rack shelving. The robotic item handler can be elevated to varying levels to permit higher or lower shelves to be accessed. Upon retrieving a tote from the rack storage, the robot must travel down the track and deposit the tote at an on/off load point. After disposing of a carried tote at the on/off load point, the robot is then free to place or pick another tote. The time for each item transfer between the on/off load point and the place/pick point includes the travel time required for the robot to move from the on/off load point to the place/pick point and back again. This system has great utility in that it provides for high density storage which is accessed by a single robot riding in a single aisle, thereby avoiding the congestion, hazard and breakage associated with human stocker systems. This strategy, while very useful, requires substantial robotic travel time, energy and wear in order for the robot to service the storage area.
It is therefore an object of the present invention to provide an automated storage and retrieval system which is faster than presently known systems.
It is a further object to provide an automated storage and retrieval system which is more efficient than known systems in terms of energy and wear.
It is yet another object to provide the aforesaid advantages without a substantial increase in cost over, or substantial modifications to, known systems.